An epoxy resin composition comprising an epoxy resin and a curing agent as essential components is excellent in various physical properties such as high heat resistance, constitutional and low viscosity and is therefore widely used for electronic and electrical components such as semiconductor sealing material and printed circuit board, conductive adhesives such as conductive paste, adhesives, matrixes for composite material, coating materials, photoresist materials and color developing materials.
In various uses, particularly advanced materials, further improvement in performances such as high heat resistance and high moisture resistance has recently been required. In the field of semiconductor sealing materials, surface mounting packages such as BGA and CSP are developed and also a reflow treatment temperature increases due to the use of a lead-free solder, and thus electronic component sealing resin materials having excellent resistance to moisture and soldering have been required furthermore.
As a technique for producing the electronic component sealing resin material which meets these required characteristics, for example, there is known a technique in which a methoxy group-containing phenol resin obtained by methoxylating a phenolic hydroxyl group in a resol resin and converting the resulting methoxylated resol resin into a novolak resin in the presence of an acid catalyst is used as a curing agent for epoxy resin, thereby to improve fluidity and to impart moderate pliability to a cured article, and thus improving moisture resistance and impact resistance of the cured article itself (see, for example, Japanese Unexamined Patent Application, First Publication No. 2004-10700).
However, such a curing agent for epoxy resin is inferior in reactivity during the curing reaction because the number of functional groups per molecule decreases.
It is of urgent necessity for a high frequency device to enable high frequency operation in the field of electronic components, and therefore electronic component-related materials such as semiconductor sealing material have low dielectric constant and materials having low dielectric dissipation factor, which have never been obtained, have recently been required. Main factor for an increase in a dielectric constant and a dielectric dissipation factor in an epoxy resin cured article is a secondary hydroxyl group, which appears during the curing reaction, and therefore lower concentration of a functional group serving as a crosslinking point is more advantageous for dielectric characteristics. In this respect, although the hydroxyl group concentration of the curing agent for epoxy resin is decreased, there has never been realized recent required level of low dielectric constant and low dielectric dissipation factor.
As a technique for producing an epoxy resin which exhibits excellent heat resistance, for example, there has been known a technique in which an aromatic compound such as anthracene as an epoxy resin used for a composite material matrix is reacted with an excess crosslinking agent such as p-xylene glycol to obtain a reaction intermediate and the resulting reaction intermediate is reacted with a phenol compound to obtain a phenol resin in which an aralkyl structure and an aromatic compound are alternately arranged, and then the resulting phenol resin is epoxidated by reacting with epichlorohydrin and used (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 8-301980).
Such an epoxy resin certainly exhibits excellent heat resistance because of high content of an aromatic structure moiety in a polymer structure. However, when the epoxy resin is used as an electronic component sealing material, there has never been realized required level of low dielectric constant and low dielectric dissipation factor. It is considered to further decrease the concentration of a functional group by further introducing an aromatic structure into the polymer chain of the epoxy resin so as to decrease the dielectric constant and dielectric dissipation factor in the epoxy resin. However, it becomes impossible to avoid drastic deterioration of curability as a result of drastic decrease in concentration of the functional group.
As described above, in the field of the electronic component-related material, there has never been obtained an epoxy resin composition having dielectric characteristics capable of coping with recent high frequency operation without causing curing hindrance.